1. Field of the Invention
The invention relates to the reinforcement of engine blocks of aluminium or aluminium alloy.
Engine blocks cast of aluminium or aluminium alloy have the primary advantage that they are light in weight in comparison with ferrous materials, so offering the opportunity of achieving high power/weight ratios in the engine. Aluminium or aluminium alloys, while having the advantage of lightness of weight have the disadvantage that they are not as strong as ferrous materials and are not as well able to withstand the stresses encountered in engine operation. One part of an engine block which is subject to particularly high stresses is the scantlings, which provide supports for the bearings of a crankshaft. These crankshaft bearings are secured in position on the scantling supports by associated caps which are bolted onto the block at the associated scantlings.
The crankshaft is loaded on either side of each scantling by the forces generated in associated connecting rods during operation of the engine. The direction and value of these forces are not the same on each side of each scantling at any one point in the engine cycle and so there is a resultant twisting force applied by the crankshaft to each scantling and its associated cap. This problem can be particularly acute where the engine is a V-configured engine, because adjacent connecting rods can generate oppositely directed forces and/or where the engine is a diesel engine, because combustion chamber pressures are higher in diesel engines than in petrol engines and thus the twisting forces are greater. The effect of these forces in combination with the direct forces is to tend to crack the aluminium or aluminium alloy of the engine block.
2. Review of the Prior Art
It has been proposed previously to form the threads for receiving the bolts holding down the caps, in reinforcements introduced into the block during casting. It has been found, however, that, although such reinforcements prevent the bolts being pulled out of their threads, they do not affect the resistance of the scantlings to the twisting forces. It has also been proposed to use two side-by-side bolts on each side of each cap or two bolts set at right angles at each side of each cap but neither of these have proved entirely satisfactory in resisting the effects of the twisting forces.
An alternative proposal has been to increase the thickness of each scantling to allow them better to resist the twisting loads. Although this offers a possibility of success, it has the disadvantages of increasing the weight, complexity and volume of the block. It is also a solution which is difficult to use where an engine block is to be uprated to take increased loads; for example, where a petrol engine block is to be converted to a diesel engine block, because, in this case, the mould or die used for producing the block will require alteration, and this can be difficult and expensive, particularly where the block is gravity die cast because redesigning such dies can be very expensive.